US 20060071385 A1
A clamping device contains a clamp jaw fixed in vertical direction, a clamp jaw moveable in vertical direction and a force transducer for applying a force to the moveable clamp jaw. The moveable clamp jaw is curved. The force transducer preferably comprises a coil and an iron core. In the non-clamping condition of the clamping device, the moveable clamp jaw is loaded with the weight of the iron core. For clamping, a current is applied to the coil that produces a magnetic field that presses the iron core against the moveable clamp jaw.
1. Clamping device, comprising
a clamp jaw fixed relative to a clamping direction,
a clamp jaw moveable in the clamping direction, the moveable clamp jaw being curved so that it forms a tapered inlet with the fixed clamp jaw, and
a force transducer for applying a force to the moveable clamp jaw, wherein in the non-clamping condition of the clamping device the force transducer exerts a first force on the moveable clamp jaw and presses the moveable clamp jaw either against the fixed clamp jaw or against an object to be clamped, and wherein in the clamping condition the force transducer exerts a second force on the moveable clamp jaw that it is stronger than the first force.
2. Clamping device according to
3. Transport mechanism for transporting a substrate in a transport direction, comprising a clamping device according to
4. Transport mechanism for transporting a substrate in a transport direction, comprising a clamping device according to
The present application claims priority under 35 U.S.C § 119 based upon Swiss Patent Application No. 1628/04 filed on Oct. 1, 2004.
The invention concerns a clamping device and a transport mechanism with such a clamping device for transporting substrates.
Such a transport mechanism is used for example on a Wire Bonder to transport substrates. A Wire Bonder is a machine with which semiconductor chips are wired by means of pressure, ultrasound and heat after they have been mounted onto a substrate. The transport mechanism comprises two guide rails, at least one clamping device moveable back and forth along the guide rails and at least one holding device. The moveable clamping device serves to transport the substrate in transport direction along the guide rails to the bonding station and away from the bonding station. The holding device serves to hold the substrate between the transport phases. The holding device is for example a rigidly arranged clamping device or a roller resting on the substrate that presses the substrate against the guide rail. The roller contains a special bearing that only allows the roller to turn in one rotational direction and blocks the roller in the opposite rotational direction. The solution with the roller is comparatively expensive and has the disadvantage that movement of the substrate in transport direction is always possible as the roller only makes movement impossible opposite to the transport direction. The rigidly arranged clamping device has the disadvantage that the clamp jaw has to be moved in order to clamp the substrate. The moved clamp jaw is a moved mass that, on impacting on the substrate, transmits a certain energy to the substrate and jolts the substrate. Especially with thin substrates—there are substrates that are only 50 micrometers thick—the vibrations can cause the bond wires of already wired semiconductor chips to deform and, under certain circumstances, neighbouring bond wires to come into contact with each other and produce an electrical short-circuit.
Transport mechanisms with fixed and/or moveable clamping devices are known from EP 330'831, CH 679'878 and CH 689'188.
The object of the invention is to develop a clamping device that on clamping does not jolt the substrate.
The construction and function of the clamping device are explained based on an example with which the object to be clamped is a substrate onto which semiconductor chips are mounted. The clamping device contains a clamp jaw fixed in vertical direction, a clamp jaw moveable in vertical direction and a force transducer for applying a force to the moveable clamp jaw. In the non-clamping condition, the force transducer has the task of applying a first, comparatively low force to the moveable clamp jaw so that the moveable clamp jaw is either in contact with the fixed clamp jaw as long as no substrate is inserted between the two clamp jaws, or is in contact with the substrate to be clamped. The moveable clamp jaw is curved so that, with the fixed clamp jaw, it forms a tapered inlet into which the substrate can be inserted without the danger of the substrate catching on the moveable clamp jaw. When the substrate is inserted into the clamping device, then the moveable clamp jaw is deflected to the extent of the thickness of the substrate: It now travels one stroke. In order to clamp the substrate, the force transducer exerts a second, greater force on the moveable clamp jaw. On changing from the non-clamping condition to the clamping condition, the moveable clamp jaw is no longer moved and therefore does not travel a stroke.
With a preferable embodiment, the force transducer comprises an iron core driven by a coil, a so-called solenoid. In the non-clamping condition of the clamping device, the moveable clamp jaw is loaded with the weight of the iron core. For clamping, a current is applied to the coil that produces a magnetic field that presses the iron core against the moveable clamp jaw.
With another embodiment, the force transducer comprises a pneumatically actuated bolt pre-tensioned by means of a spring. The spring presses the bolt against the moveable clamp jaw. To clamp the substrate, pneumatic pressure is additionally applied to the bolt so that the force exerted by the bolt on the moveable clamp jaw is increased.
The clamping device is particularly suited for use in a transport mechanism for transporting substrates in a predetermined transport direction.
The accompanying drawings, which are incorporated into and constitute a part of this specification, illustrate one or more embodiments of the present invention and, together with the detailed description, serve to explain the principles and implementations of the invention. The figures are not to scale. In the drawings:
The transport mechanism is particularly suitable for use on a Wire Bonder where semiconductor chips mounted on the substrate 1 are wired to the substrate 1 in the processing station 8. In technical jargon the processing station is called a bonding station.
When the substrate 1 is transported in transport direction 2 and reaches the clamping device then, on inserting the substrate 1 into the clamping device, the plate 17 and the iron core 22 are moved in z direction. The curved form of the plate 17 forms a tapered inlet and ensures that the substrate 1 does not catch on insertion. The iron core 22 now presses with its own weight against the plate 17 and therefore also against the substrate 1. This condition is shown in
The invention can also be implemented with a clamping device that is moveable back and forth along the guide rail 4. The clamping device is constructed identically to the clamping device explained based on
The force transducer comprising the coil 21 and the iron core 22 can be replaced by a pneumatic force transducer that has a bolt to which pressure can be applied and which is pre-tensioned with a spring. This solution is particularly suited when the clamping device does not run in vertical direction.
While embodiments and applications of this invention have been shown and described, it would be apparent to those skilled in the art having the benefit of this disclosure that many more modifications than mentioned above are possible without departing from the inventive concepts herein. The invention, therefore, is not to be restricted except in the spirit of the appended claims and their equivalents.